A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and hydrogen in a hydrocarbon-based material such as methanol, ethanol, or natural gas.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The DOFC includes a direct methanol fuel cell that uses methanol as a fuel.
The PEMFC provides a relatively high energy density, but it requires careful handling of hydrogen (or hydrogen-rich) gas and accessories such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce the hydrogen (or hydrogen-rich) gas as a fuel for the PEMFC.
In comparison, a DOFC provides a lower energy density than that of the PEMFC. However, the DOFC advantages include easy handling of a fuel, operability at room temperature due to its low operating temperature, and no need for additional fuel reforming processors.
In the above fuel cell systems, a stack that generates electricity includes several to scores of unit cells stacked in multiple layers, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) attached to each other with a polymer electrolyte membrane located between them. The polymer electrolyte membrane includes a proton conductive polymer.